What does "Full-stack" mean?

Full-stack:

A full-stack developer is one who can create both the front-end (what people see when they view your website) and the back-end (the system for creating and showing pages out of a database, for instance). Most website developers are not full-stack in that they only know how to make a website using WordPress or WIX. A full-stack developer will be able to help a client determine what is needed technically to achieve the purpose of a website and then put it in place.

 W3 Schools: Full Stack

 Geeks for Geeks: Full-stack